Car tyres are often taken for granted. You turn the steering wheel, your car takes the corner, you press the brake, your car stops. This is fine but knowing how car tyres work and the characteristics they generate in terms of handling and roadholding is both interesting and potentially helpful to your driving.
Every car tyre has an area of tread, about the size of an adult’s footprint, in contact with the road surface. This is called, somewhat predictably, its contact patch. Imagine the tyres’ four contact patches travelling along a road in a straight line. These four areas of tread are what keep your car on the road, allowing you to accelerate, steer and brake with confidence.
Now, what happens to car tyres in corners? Imagine the wheels following the arc that the corner represents. The wheels will be following the arc faithfully, but there’s a hidden force at work. Imagine you’re Superman and have X-ray vision. Looking down at the top of a wheel and tyre combination, you’d see that the contact patch will be following a tighter curve than the wheel is following.
So, what’s happening? Why the difference? It’s there because sideways force put on the tyre by the weight of the car is deforming the car tyre’s carcass. Now, imagine a straight line drawn through the centre of the wheel and another drawn through the centre of the contact patch. There will be a difference between the two – this difference is called the slip angle.
As slip angles increase, the car tyre’s grip increases, up to a point. When the forces involved head towards the maximum level of grip the car tyres offer, one of three states will apply. Say the slip angles are equal at both ends of the car. In this case, the grip at each end of the car will be the same. When the grip level’s limit is reached, the car will go into a classic, four-wheel drift. The car’s handling will be ‘neutral’. Racing cars are set up to give neutral handling.
Supposing the slip angles of the car tyres at the front are greater than those at the rear. Then, the driver will need to apply more steering input to make the car follow the chosen curve. This is called ‘understeer’.
When it reaches the limit of effective grip of its car tyres, an understeering car will slide off the track forwards – it simply won’t be able to corner tightly enough. In practice, most road cars understeer. Why? Because understeer is a generally controllable condition – it’ll help scrub off excess speed when a corner is taken too enthusiastically.
The third state occurs when the rear car tyres’ slip angles are greater than those of the front tyres. The rear tyres will be giving less grip than the front ones. At the limit, the car’s tail will slide towards the outside of the curve. When you see a Formula One car or Touring Car spin off a track, it’s gone beyond oversteer.
This explanation is necessarily basic. In fact, very many parameters affect how car tyres respond to the forces imposed upon them. However, the physics are just as basic, and give car designers benchmarks from which to work.
Article Resource
Merityre.co.uk are one of the leading UK independent suppliers of car tyres. Why not visit their website for an online tyre quote or contact your nearest fitting centre.
Monday 13 August 2012
Super Savers. Keeping Car Tyre Costs Down
Depressing as it may be, the tottering economic situation, in this country and across much of the world, is a fact. This means we must live with it but we needn’t merely accept it passively. We can take active steps to keep costs down, and in regard to our motoring and especially our car tyres, there are plenty of tips and tricks for saving money.
Efficiency Counts
The deductive powers of a Sherlock Holmes aren’t needed to figure out where car tyre factors could be costing us money. The key word is ‘efficiency’, and here’s how inefficiency can affect motoring costs.
All cars give a certain power output. Whether this is quoted in kilowatts, pferdestärke or good old horsepower is irrelevant, power can be wasted by inefficiency. A certain amount of power is required to make a car progress, and anything that impedes this progression is wasteful. Under inflated car tyres require more power to make progress, because the lesser tyre pressure increases their rolling resistance. Run your car tyres at the correct pressure, or even a little higher, and you’ll soon see rewards at the fuel pump.
Of course, it isn’t just car tyres that can cause drag, which in turn increases fuel consumption. The current warm weather makes it tempting to use the car’s air conditioning. Would you use it so readily if you knew it could worsen your car’s fuel consumption by up to 11 per cent? You could open some windows, but this creates aerodynamic drag – it seems you can’t win. In fact, it makes sense to cool the car interior by opening the windows at slower speeds. When motoring at 40mph or over, use the aircon – it costs less.
Weight Issues
All car tyres create some drag, that’s also a fact. All car tyres also carry weight, and it’s a fact that the amount they carry can be trimmed, in some cases radically. What you carry on a regular basis in your car depends largely on how you use your car. That said, a lot of people carry unnecessary objects in the car at all times. You could argue that you really need your Wellington boots, snow shovel, overcoat and Thermos flask on board. Well, argue away – you’re carrying what represents dead weight for August and it’s you who are buying the fuel. A combination of ruthlessness and good sense about what lives in the car and when isn’t hard to apply.
Similar thinking should apply to your car’s roof rack or roof box. Sure, it’s well away from your car tyres but what’s on the roof costs you fuel simply by being their. Each has a weight, which you’re paying to transport. Each has a degree of air resistance, even if your roof box has sexy, aerodynamic styling. Again, you’re paying to push that roof-mounted deadweight through the air. Remove it when not in use and your pocket will thank you.
Obvious Strategies
There are a more fuel wasters than car tyre rolling resistance. Driving too hard and/or too fast when you needn’t are money guzzlers, as are speed camera fines and the increased insurance cost of points on your licence. Use the most efficient route, use the highest possible gear and above all, use your head. Everything in this article comes under a single heading, common sense.
Article Resource
Merityre.co.uk are one of the leading UK independent suppliers of car tyres. Why not visit their website for an online tyre quote or contact your nearest fitting centre.
Efficiency Counts
The deductive powers of a Sherlock Holmes aren’t needed to figure out where car tyre factors could be costing us money. The key word is ‘efficiency’, and here’s how inefficiency can affect motoring costs.
All cars give a certain power output. Whether this is quoted in kilowatts, pferdestärke or good old horsepower is irrelevant, power can be wasted by inefficiency. A certain amount of power is required to make a car progress, and anything that impedes this progression is wasteful. Under inflated car tyres require more power to make progress, because the lesser tyre pressure increases their rolling resistance. Run your car tyres at the correct pressure, or even a little higher, and you’ll soon see rewards at the fuel pump.
Of course, it isn’t just car tyres that can cause drag, which in turn increases fuel consumption. The current warm weather makes it tempting to use the car’s air conditioning. Would you use it so readily if you knew it could worsen your car’s fuel consumption by up to 11 per cent? You could open some windows, but this creates aerodynamic drag – it seems you can’t win. In fact, it makes sense to cool the car interior by opening the windows at slower speeds. When motoring at 40mph or over, use the aircon – it costs less.
Weight Issues
All car tyres create some drag, that’s also a fact. All car tyres also carry weight, and it’s a fact that the amount they carry can be trimmed, in some cases radically. What you carry on a regular basis in your car depends largely on how you use your car. That said, a lot of people carry unnecessary objects in the car at all times. You could argue that you really need your Wellington boots, snow shovel, overcoat and Thermos flask on board. Well, argue away – you’re carrying what represents dead weight for August and it’s you who are buying the fuel. A combination of ruthlessness and good sense about what lives in the car and when isn’t hard to apply.
Similar thinking should apply to your car’s roof rack or roof box. Sure, it’s well away from your car tyres but what’s on the roof costs you fuel simply by being their. Each has a weight, which you’re paying to transport. Each has a degree of air resistance, even if your roof box has sexy, aerodynamic styling. Again, you’re paying to push that roof-mounted deadweight through the air. Remove it when not in use and your pocket will thank you.
Obvious Strategies
There are a more fuel wasters than car tyre rolling resistance. Driving too hard and/or too fast when you needn’t are money guzzlers, as are speed camera fines and the increased insurance cost of points on your licence. Use the most efficient route, use the highest possible gear and above all, use your head. Everything in this article comes under a single heading, common sense.
Article Resource
Merityre.co.uk are one of the leading UK independent suppliers of car tyres. Why not visit their website for an online tyre quote or contact your nearest fitting centre.
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